LAYERED THERMAL BARRIER COATING AND COATING METHOD

Field of the Invention

The present invention relates to a layered thermal barrier coating, which enables heat insulation of cylinder head, piston, valve, exhaust/intake port and/or engine cylinder wall components in diesel engines, and which, by reducing the heat transfer via these components to the cooling and lubricating system, enables to increase the useful heat that will be utilized; and to a method for providing this coating.

Background of the Invention A part of the heat obtained as a result of combustion in diesel engines passes to the cooling and lubricating systems via the engine components. In order to prevent this situation, which causes the engine components to be destroyed as a result of overheating and the amount of useful heat that can be utilized to decrease, thermal barrier coating applications are developed. In the state of the art, by applying ceramic containing thermal barrier coating on the piston, cylinder wall, valve, cylinder head and exhaust/intake port components which are exposed to high combustion temperatures, heat transfer to/from the said components is reduced. In addition to reducing the heat transfer to the cooling and lubricating systems, this application also protects the engine components against the influences of high heat.

In the current art, due to the porous structure of the thermal barrier coating, penetration of the fuel to the porous structure formed on the combustion surface causes delayed combustion. United States patent document no. US4852542, an application in the state of the art, discloses a thermal barrier coating of a specified thickness of 0.002 to 0.009 inch to insulate the combustion chamber of an internal combustion engine to achieve optimum reduction of transient head flow.

United States patent document no. US5413877, an application in the state of the art, discloses an engine block comprising thermal barrier and wear coating. The thermal barrier is applied to the engine cylinder surface to reduce the waste heat amount. Thus it reduces the need for air or liquid cooling.

German patent document no. DE102010034655, an application in the state of the art, discloses an engine having an engine block coated by a heat insulating material. The heat insulating material directly rests against the engine block. International patent document no. W09324672, an application in the state of the art, discloses a thermal barrier coating for metal articles subjected to rapid thermal cycling.

Summary of the Invention

The objective of the present invention is to provide a layered thermal barrier coating in diesel engines; which is applied on the cylinder head, piston, exhaust/intake port and engine cylinder wall components and thereby enables the heat transfer from the said components to the cooling and lubricating system to be reduced; and a coating method.

Another objective of the present invention is to provide a layered thermal barrier coating in diesel engines, which prevents penetration of the fuel into the thermal barrier layer, and a coating method. A further objective of the present invention is to provide a layered thermal barrier coating in diesel engines, which prevents penetration of the fuel to the pores, on the thermal barrier layer and accordingly prevents delay of combustion by means of a final layer that is applied on a normal thermal barrier layer, and a coating method.

Detailed Description of the Invention

"Layered thermal barrier coating and coating method in diesel engines" developed to fulfill the objective of the present invention is illustrated in the accompanying figures, wherein;

Figure 1 is a view of the cylinder head, cylinder wall, piston, valve, exhaust/intake port in a diesel engine section.

Figure 2 a sectional view of the layered thermal barrier coating of the present invention.

The components given in the figures are assigned reference numbers as follows:

1. Layered thermal barrier coating

2. Metal surface

3. Bonding layer

4. Thermal barrier layer

5. Final layer

D. Diesel engine

H. Cylinder head

C. Cylinder wall

P. Piston

V. Valve

E. Exhaust/intake port The layered thermal barrier coating (1) of the present invention; which, in diesel engines, enables to reduce the heat transfer to the lubricating and cooling systems and to prevent delay -of combustion resulting due to penetration of the fuel to the piston (P), valve (V) and cylinder head (H) surface; comprises

- a metal surface (2) which is used in production of diesel engine (D) part and on which the coating application will be performed,

- a bonding layer (3) which is applied on the metal surface (2) before the thermal barrier layer (4) and which both enables the thermal barrier layer (4) to be firmly attached to the metal surface (2) and prevents the thermal barrier layer (4) from getting broken due to the different expansion coefficients of the metal surface (2) and the thermal barrier layer (4),

- at least one thermal barrier layer (4) which enables to reduce the heat transfer to the metal surface (2) by means of its porous structure by being applied on the bonding layer (3),

- a final layer (5) which is applied on the thermal barrier layer (4) thereby eliminating the porosity caused by the porous structure of the thermal barrier layer (4), and which thus prevents the fuel from penetrating into the thermal barrier layer (4) particularly at the piston (P), valve (V) and cylinder head (H).

In the preferred embodiment of the invention, thickness of the bonding layer (3) can be optimized according to the metal surface (2) on which it will be applied and generally varies between 50μπι-150μηι. In the preferred embodiment of the invention, NiCr alloys are used for the bonding layer (3), which alloys are comprised of 16-21% by weight of chrome, 15-20% by weight of different metal elements, and nickel for the remaining amount. In the preferred embodiment of the invention, the bonding layer (3) is produced from a material or a mixture of materials selected from a group comprising NiAl, NiCrAl, NiCrAlY and NiCrMo materials. In the preferred embodiment of the invention, the thickness of the thermal barrier layer (4) can be optimized according to the surface on which it will be applied and the desired heat transfer amount, and generally varies between 200μπι-300μηι.

In the preferred embodiment of the invention, the thermal barrier layer (4) is produced from a material or a mixture of materials selected from a group consisting of zirconium, yttrium, aluminum and magnesium oxides.

In the preferred embodiment of the invention, the final layer (5) is produced from a material similar to the bonding layer (3). In the preferred embodiment of the invention, the final layer (5), similar to the bonding layer (3), is produced from NiCr alloys, which are comprised of 16-21% by weight of chrome, 15-20% by weight of different metal elements and nickel for the remaining amount. Preferably, the final layer (5) is produced from a material or a mixture of materials selected from a group comprising NiAl, NiCrAl, NiCrAlY and NiCrMo materials.

In the preferred embodiment of the invention, a material or a mixture of materials selected from a group comprising iridium, palladium, platinum and rhodium, which serves as a catalyst for combustion and thus accelerates combustion, is added into the final layer (5).

In the preferred embodiment of the invention, thickness of the final layer (5) varies between 10μ-30μιη in order to optimally eliminate the porosity in the thermal barrier layer (4). The layered thermal barrier coating method comprises the steps of

- washing the metal surface (2) that will be coated, - heating the metal surface (2) in order to remove the oil and moisture remaining thereon,

- roughening the metal surface (2) by spraying sand on the metal surface (2) that will be coated,

- coating the roughened metal surface (2) by the bonding layer (3),

- forming the thermal barrier layer (4) on the bonding layer (3) surface by a ceramic based material,

- coating the thermal barrier layer (4) with a final layer (5) in order to eliminate the porosity caused by the porous inner structure of the thermal barrier layer (4),

- processing the final layer (5) according to the desired surface roughness.

In the preferred embodiment of the invention, in the step of heating the metal surface (2) in order to remove the oil and moisture remaining thereon, the metal surface (2) is heated to a temperature of 150 °C-200°C.

In the preferred embodiment of the invention, in the step of coating the roughened metal surface (2) with the bonding layer (3), a nonporous bonding layer (3) which has improved micro and macro hardness levels and high abrasion and corrosion resistance is produced by performing the coating process via plasma spray method.

This thermal barrier coating application, which is widely used in turbines, and which also includes the present invention, is basically comprised of the following stages: roughening the metal surface (2) in order to enable the coating (1) to be firmly attached to the metal surface, applying the bonding layer to the roughened surface, applying the thermal barrier layer (4) onto the bonding layer (3), and applying a nonporous final layer (5) on the thermal barrier layer (4) in order to eliminate the pores. Coating process is generally performed via spraying method. Within the framework of the layered thermal barrier coating method of the present invention, thermal barrier layer (4) is applied on the components such as cylinder head (H), piston (P), valve (V), exhaust/intake port (E) and cylinder wall (C) in diesel engines (D). By means of the coating (1) that is applied, heat transfer from the said components to the cooling and lubricating system is reduced and/or combustion is accelerated.

The bonding layer (3) both enables the thermal barrier coating material (4) to get attached to the metal surface (2), and prevents the breakages that may occur on the thermal barrier layer ^" (4) due to the different expansions between the main material forming the metal surface (2) and the thermal barrier layer (4) material.

Penetration of the fuel into the surface due to the porous structure of the thermal barrier layer (4) is prevented thanks to the layered thermal barrier coating (1) in diesel engines (D), by means of using a final layer (5) produced from a material similar to the bonding layer (3) on the thermal barrier layer (4). This way, delayed combustion is prevented. Furthermore, by means of the catalytic materials added into the final layer (5) combustion can be accelerated. Thanks to the layered structure of the present invention, penetration of the fuel into the surface pores will become difficult or be prevented. Thickness values of the layers (3, 4, 5) given for each stage are given as a range. Coating thicknesses may vary according to the desired application area.